Numerical Simulations Of Crustal Melting And Rheology And Theirs Geological Constraints

Unobserved of geological processes inside the Solid-Earth is the fundamental reason for long time argument with many important geological problems.One of the problems is granite(generalized)genesis.The development of numerical simulation and super computing technology provides the possibility for the geological process of the crust,including digital reconstruction of granite formation.A large number of studies have been carried out for numerical simulation of granite "anatexis-intrusion" geological model.Thus,this paper is based on "anatexis-convection" geological model,using the long-term geodynamics simulation platform-Underworld and Tianhe-2supercomputer,carry out a numerical simulation research of thermal dynamic process of granite formation,and crustal deformation effect in this process.This topic is not only for digital reconstruction the process of granite formation with important geological significance,but also is the important link to quantitative study of Geology in Big-Data times.In order to understand the rheological behavior of partial melting rocks,the author comprehensive analysis the relationship between melt fraction and rock strength changes of the experimental data onto various rock in the partial melting process,puts forward the research the continental crust anatexis of rock should be used "aggregate strength" understanding.Base on this,the corresponding melt fraction(MF)of "melt connectivity transition"(MCT)and the "solid-liquid transition"(SLT)have been re-determined.Meanwhile,it is found that there is a sudden drop in the aggregate strength of rock at MF=25%,and term it as "framework-melting transition"(FMT).The second part of this paper is about the study.By means of field measurement on the migmatite-granite profile of Fuhu hill,SE China and indoor calculation,the leucosome proportion of each kind of migmatite and granite on this profile is obtained.Using rock rheological behavior obtained by analyzed from the experimental data combined with the geological data on the Fuhu profile,realize bidirectional constraint between the rheological transition points and geological phenomenon.Base on above and according to the constrained rheological transition point "SLT",the author established the mathematical expression of melting process of rock,and used this mathematical relation of numerical simulation to verify the feasibility and universality of "anatexis-convection" geological model and analysis the rheological phenomenon of it.The conclusions of this study aresummarized as follows:(1).There are three rapid drops of "aggregate strength" between solidus and liquidus in rock melting process,i.e.MCT,FMT and SLT.The respective melt fraction percentages correspond to 8%,25% and 40%;(2).By comparison with Fuhu migmatite-granite profile found that in crustal melting process,the MCT marks the intergranular melts transfer from pore space to foliation(bedding,schistosity,etc.)space,which leads to layered structure or banded structure in partial melting rock.The "FMT" marks the transition of the solid framework from compaction to fusion in partial melting.Geochemically,it is the melting transition marks that from eutectic mineral to refractory mineral.The SLT indicates the disintegration of solid framework of rock,which marks the rock state transition from solid state to liquid state(magma).In the partial melting process(anatexis)of the salic crust,the magma as layer like should be appeared under the depth of SLT.And there is no longer having continuous rocks under this depth;(3).The simulation results of the continental crust melting process shows that the magma convection occurs under the SLT,and the convection can lead to the constant thickening of the continental melting layer.The velocity of magma convection is dependent on the bottom boundary temperature of the model,and the convection occurred only if this temperature large than 739.6?.The linear variation of the bottom boundary temperature of the model can lead to the magma convection from the independent vortex to the overall circulation;(4).The dragging effect on crustal cover by magmatic flowed,not only causes the fluctuation of the magma interface,but also leads to horizontal stress environment in cover play as compression and extension alternating appeared.The former reflects the response of cover deformation to magmatic flowed.The latter indicates that the change of horizontal stress in solid cover,can be the result of magma convection rather than it caused the magma flow.Simulation shows that the shear force between magma flow and cover can cause the deformation of partial melting rock which lies above on the melting layer.This result reveals that the deformation of partial melting rock can be simply caused by magmatic flowed and no necessarily need regional tectonic dynamics;(5).Numerical simulation of compression process of the crust which contains magma layer,reveals anisotropic of the velocity of magmatic flowed can cause uneven deformation of the crustal cover,and shows the undulating magma interface(SLT)and the deformation of ground has the same direction.Thus,it reveals that the "anatexis-convection" geological model concerning the formation mechanism of granite and migmatite dome and anticline;(6).The numerical simulation results show that the "anatexis-convection" geological model conforms to the basic physical laws,and it is universality on interpretation of the relevant geological phenomena.